Combustion studies on ammonium perchlorate/trimethylammonium perchlorate mixtures

A study of the burning rates of compressed mixtures of ammonium perchlorate (AP) and trimethylammonium perchlorate (TMAP) has been carried out at ambient pressure. The overall increase in the linear burning rate, showing a maximum at a composition having 80% TMAP, has been discussed in terms of factors such as stoichiometry, presence of faster burning component, and eutectic melt formation. The thermal decomposition studies of the mixtures, using isothermal thermogravimetry and differential thermal analysis techniques, indicate the possibility of eutectic melt formation.

A novel combustion process for the synthesis of fine particle α-alumina and related oxide materials

Synthesis of fine particle α-alumina and related oxide materials such as MgAl2O4, CaAl2O4, Y3Al5O12 (YAG), Image , β′-alumina, LaAlO3 and ruby powder (Image ) has been achieved at low temperatures (500°C) by the combustion of corresponding metal nitrate-urea mixtures. Solid combustion products have been identified by their characteristic X-ray diffraction patterns. The fine particle nature of α-alumina and related oxide materials has been investigated using SEM, TEM, particle size analysis and surface area measurements.

Thermochemistry and lower combustion limit of ammonium perchlorate in presence of methylammonium perchlorates

The heats of combustion of mono-, di-, tri- and tetramethylammonium perchlorates have been determined by bomb calorimetry. The data have been used to explain why the thermal behavior of ammonium perchlorate (AP) is considerably modified in presence of these compounds as shown by differential thermal analysis. Above a particular concentration of methylammonium perchlorate (MAP), AP ignites in a single step around 290°C. The minimum concentration of a MAP (mono-, di-, tri- or tetra-) needed to cause ignition of AP in a single step depends on intramolecular “elemental stoichiometric coefficient” of the mixtures that has the same value regardless of the MAP. Furthermore, the calorimetric values of these mixtures are the same. The heat evolved on ignition of such a composition appears to determine the lower concentration limit of combustion of its mixture with AP.

Pyrolysis and combustion of alpha-cellulose: effect of dihydrazinium phosphate (N2H5)2HPO4

A strip of Whatman filter paper (α-cellulose) dipped in an aqueous solution of dihydrazinium phosphate, (N2H5)2HPO4(DHP), and dried, carbonized without flame when ignited. The observed flame retardancy of DHP on α-cellulose has been studied using TG, DTA and mass spectrometry. Dihydrazinium phosphate appears to catalyze the dehydration of α-cellulose, minimizing the depolymerization which produces flammable tars, with the formation of water and char. Flame retardancy of DHP is compared with that of diammonium phosphate and phosphoric acid.

Combustion and Thermal Decomposition of a Binary Oxidiser System: Ammonium Perchlorate-Potassium Perchlorate

Combustion behaviour of ammonium perchlorate-potassium perchlorate pellets is studied using Crawford strand burners. At low concentrations of potassium perchlorate (up to 30 percent potassium perchlorate) the burning rate of ammonium perchlorate-potassium perchlorate condensed mixtures increases with potassium perchlorate content. Above 40 percent potassium perchlorate content, combustion sustenance becomes difficult. Decomposition products of ammonium perchlorate sensitize the melting and subsequent decomposition of potassium perchlorate. The results are explained in terms of the melt layer thickness, flame temperature and the resultant surface temperature, and heat wave penetration into the solid. The study suggests the importance of melt layer on the burning surface in the deflagration behaviour of ammonium perchlorate-potassium perchlorate condensed mixtures

Analysis and computation of the oil film thickness between the piston ring and cylinder liner of an internal combustion engine

A study of the essential features of piston rings in the cylinder liner of an internal combustion engine reveals that the lubrication problem posed by it is basically that of a slider bearing. According to steady-flow-hydrodynamics, viz. Image the oil film thickness becomes zero at the dead centre positions as the velocity, U = 0. In practice, however, such a phenomenon cannot be supported by consideration of the wear rates of pistion rings and cylinder liners. This can be explained by including the “squeeze” action term in the

Thermal decomposition and combustion of ammine: AP pellets

Thermal decomposition and combustion of lithium perchlorate ammine:ammonium perchlorate (LPA:AP) and magnesium perchlorate ammine:ammonium perchlorate (MPA:AP) pellets have been studied using DTA, TG, and strand burner techniques. The DTA results of the ammine:AP pellets show that the addition of ammines lowers the ignition temperature of AP. However, isothermal TG of the ammine:AP pellets show that in the case of LPA:AP pellets the extent of decomposition increases with the increase in the concentration of LPA; whereas in the case of MPA:AP pellets the extent of decomposition decreases with the increase in the concentration of MPA. Similarly, LPA:AP pellets show higher burning rates compared to AP pellets. On the other hand, MPA:AP pellets show lower burning rates compared to AP pellets. Increasing the concentration of MPA in MPA:AP pellets completely suppresses the combustion. These results are explained on the basis of the thermal characteristics of the additives and their decomposition products.

Drag reduction by counterflow supersonic jet for a blunt cone in high enthalpy flows

Counterflow supersonic jet is used as a drag reduction device during the experiments in free piston driven shock tunnel, HST3. Accelerometer based force balance is employed to measure the drag force experienced by the 60-degree apex angle blunt cone model without and with the supersonic jet opposing the hypersonic flow. It is observed that the drag force decreases with increase in injection pressure ratio until the critical injection pressure is reached. Maximum reduction in drag force of 44 percent is recorded at the critical injection pressure ratio 22.36. Further increase in injection pressure ratio has reduced the percentage drag reduction. Change in nature of the flowfield around the model has also been observed across the critical injection pressure ratio.

Experimental and numerical investigation of jet injection in a wall bounded supersonic flow

Numerical and experimental studies of a supersonic jet (Helium) inclined at 45 degrees to a oncoming Mach 2 flow have been carried out. The numerical study has been used to arrive at a geometry that could reduce an oncoming Mach 5.75 flow to Mach 2 flow and in determining the jet parameters. Experiments are carried out in the IISc. hypersonic shock tunnel HST2 at similar conditions obtained from numerical studies. Flow visualization studies carried out using Schlieren technique clearly show the presence of the bow shock in front of the jet exposed to supersonic cross flow. The jet Mach number is experimentally found to be approximate to 3. Visual observations show that the jet has penetrated up to 60% of the total height of the chamber.

Combustion and Thermal Decomposition of Ammonium Perchlorate-Aluminium Composite Pellets: Mechanism for Aluminium Participation

Thermal behaviour of ammonium perchlorate-aluminium composites is studied using differential thermal analysis, thermogravimetry and differential scanning calorimetry. Electrical resistivity studies throw light on the mechanism of ammonium perchlorate decomposition at different aluminium contents. The differences observed in burning behaviour by earlier authors is explained in terms of porosity and thermal conductivity of the composite.

Rocket Propellant Combustion Studies in a Constant Volume Bomb

A constant volume window bomb has been used to measure the characteristic velocity (c*) of rocket propellants. Analysis of the combustion process inside the bomb including heat losses has been made. The experiments on double base and composite propellants have revealed some (i) basic heat transfer aspects inside the bomb and (ii) combustion characteristics of Ammonium Perchlorate-Polyester propellants. It has been found that combustion continues even beyond the peak pressure and temperature points. Lithium Fluoride mixed propellants do not seem to indicate significant differences in c*) though the low pressure deflagration limit is increased with percentage of Lithium Fluoride.

The problem of liquid droplet combustion-reexamination

The simple quasi-steady analysis of the combustion of a liquid fuel droplet in an oxidising atmosphere provides unsatisfactory explanations for several experimental observations. It's prediction of values for the burning constant (K), the flame-to-droplet diameter ratio ( ) and the flame temperature (Tf) have been found to be amgibuous if not completely inaccurate. A critical survey of the literature has led us to a detailed examination of the effects of unsteadiness and variable properties. The work published to date indicates that the gas-phase unsteadiness is relatively short and therefore quite insignificant.A new theoretical analysis based on heat transfer within the droplet is presented here. It shows that the condensed-phase unsteadiness lasts for about 20â??25% of the total burning time. It is concluded that the discrepancies between experimental observations and the predictions of the constant-property quasi-steady analysis cannot be attributed either to gas-phase or condensed-phase unsteadiness.An analytical model of quasi-steady droplet combustion with variable thermodynamic and transport properties and non-unity Lewis numbers will be examined. Further findings reveal a significant improvement in the prediction of combustion parameters, particularly of K, when consideration is given to variations of cp and λ with the temperature and concentrations of several species. Tf is accurately predicted when the required conditions of incomplete combustion or low ( ) at the flame are met. Further refinement through realistic Lewis numbers predicts ( ) meaningfully.

Combustion and thermal decomposition characteristics of composite solid propellants

The role of thermal decomposition of the binder and the oxidiser in the thermal decomposition, ageing and combustion of composite solid-propellants has been investigated. The present study shows that the burning rate and ageing of polystyrene and ammonium perchlorate propellant are related to the thermal decomposition of the propellant itself and ammonium perchlorate.